1. Field of the Disclosure
The present disclosure relates to the field of temperature control, and more particularly, to maintaining a set point temperature of an electronic device through heating and/or cooling of the electronic device or component, typically while the electronic device or component is under test.
2. Background Information
Solid state electronic devices or components, such as semiconductors, have varying performance characteristics based on temperature. Typically, for example, such electronic devices generate heat (i.e., self-heat) during operation, and thus as the internal temperature increases, the performance characteristics change. Also, solid state electronic devices may be used in different environments, possibly enduring a wide range of temperatures.
To ensure constant performance characteristics, it is desirable to maintain a relatively constant temperature of electronic devices. This is especially true when functionally testing electronic devices to ensure proper operation and compliance with design specifications. For example, an electronic device, referred to as a device under test (DUT), may undergo endurance procedures, such as short-circuit testing and burn-in testing, to observe various device characteristics. During such testing, the temperature of the DUT must be kept relatively constant at a predetermined test temperature, or set point temperature, in order for the results to be meaningful. In other words, the tester must be able to confirm that certain observed electrical characteristics are attributable to factors other than changing temperatures.
In order to maintain a constant temperature, known thermal control devices are capable of removing heat, e.g., through a heat sink, as well as adding heat, e.g., through an electric heater. A heat sink incorporates a fluid having a temperature much lower than the test temperature of the DUT. A heater is placed between the DUT and the heat sink, and power is applied to the heater to raise the temperature of the heater face, e.g., to the test temperature required for DUT testing. The heat sink offsets any excess heating, and also removes heat generated by the DUT during the testing process, to the extent this self-heating increases the device temperature beyond the test temperature. Power fluctuations may cause significant and relatively instantaneous self-heating, requiring the need for the thermal controller to quickly and accurately react to offset the unwanted increase in temperature.
However, the total amount of power that can be removed is limited by the heater itself, which has a maximum for power density (or Watt Density). For example, if a heater is capable of operating at 500 Watts, then approximately half of that power may be lost through the heat sink into the colder fluid simply to maintain the test temperature. Thus, for example, 250 Watts are required to maintain test temperature. Then, if power in the heater is reduced to zero in response to power being applied to the DUT, the maximum amount of power which can be removed from the DUT is 250 Watts. Otherwise, the heater will be unable to offset heat removed through the heat sink. This is particularly problematic in that current requirements of DUT testing have risen to 500 Watts total power and are projected to be higher in the future. Additionally, the heater also adds unwanted thermal resistance, adds thermal mass, induces gradients (non-thermally uniform surface) and renders an inadequate response time.
Improvements to this type of thermal controller are difficult to implement. For example, the heat sink must be appropriately balanced to the heater, which may be a disincentive for improving heat sink efficiency. That is, if the heat sink's heat removal capability is improved, e.g., by increasing fluid flow through the heat sink, reducing the fluid temperature, improving fin efficiency and/or incorporating a more effective fluid, the heater capacity would likewise need to be increased to offset the improvements in cooling capabilities and maintain the testing temperature.
Other thermal controllers are not necessarily dependent on the combination of heat sinks and heaters, but they still have functional inefficiencies. For example, Peltier devices create heat differentials from electric voltages, effectively acting as both a heat sink and a heat source. A drawback of Peltier devices, though, is that they are unable to remove significant power or to handle high power densities because the response time required to dynamically react to and remove power from an electronic device is inadequate.
Further, thermal controllers that mix fluids having different temperatures to maintain the set point temperature, or a target temperature, of the DUT during a testing of the DUT have drawbacks as well. When two fluids at different temperatures are combined, a thermal controller system, including e.g., a chiller(s) and/or a heater(s), has to recover the energy lost from the mixing of the fluids at two different temperatures and must compensate for the lost energy by re-cooling/re-heating the fluids before the fluids are recirculated through the thermal controller system during testing of the DUT. One such device is disclosed in International Application Number PCT/US07/74727, the disclosure of which is expressly incorporated herein by reference in its entirety. To recover the energy lost, the thermal controller system must work hard to separate, re-cool and re-heat the previously mixed fluid to achieve each fluid's original temperature before being combined.
Therefore, a need exists for a simplified thermal controller system that meets the demands of maintaining a target temperature of an electronic device under test, that minimizes energy loss, and that maximizes cyclical efficiency (i.e., does not require the system to work harder to recover the lost energy). There is also a need for a thermal controller system that reduces costs and minimizes required equipment.